In many traditional retail establishments, a cashier receives items to be purchased and scans them with a UPC scanner. The cashier insures that all the items are properly scanned before they are bagged. As some retail establishments incorporate customer self-checkout options, the customer assumes the responsibility of scanning and bagging items with little or no supervision by store personnel. A small percentage of customers have used this opportunity to defraud the store by bagging items without having scanned them or by swapping an item's UPC with the UPC of a lower priced item. Such activities cost retailers millions of dollars in lost income. There is therefore a need for safeguards to independently confirm that the checkout list is correct and discourage illegal activity while minimizing any inconvenience to the vast majority of honest and well-intentioned customers that properly scan their items.